One such two-stage supercharging electric-assist turbocharger has been disclosed in the following Patent document 1.
In the turbocharger disclosed in the Patent document 1, a two-stage supercharging compressor section is constructed by a first compressor stage and a second compressor stage arranged adjacent to each other. An electric motor is arranged on the side of the first compressor stage, whereas an exhaust-gas turbine section is arranged on the side of the second compressor stage, in a manner so as to sandwich the first and second compressor stages between the electric motor and the turbine section. The turbine section is driven by exhaust gas energy. The first compressor wheel, the second compressor wheel, the motor rotor, and the turbine wheel are integrally coupled to a same, common shaft.
A first flow passage is provided outside of a stator (stator coils) of the motor for introducing air through the first flow passage into the suction side of the first compressor stage. Also provided is an intercooler (i.e., a heat exchanger) installed in a second flow passage, through which the pressure side of the first compressor stage and the suction side of the second compressor stage are connected to each other.